This project seeks to characterize how the interaction between transfer RNA (tRNA) and cytochrome c (cyt c) modulates apoptosis of cancer cells. tRNA and cyt c are ancient molecules with fundamental roles in biology. In healthy cells the major function of tRNA and cyt c are to interpret the genetic code by connecting amino acids to anticodons and to transport electrons in oxidative phosphorylation, respectively. Cyt c is also a defining player in the intrinsic apoptosis pathway, which is critical for protection from cancer. W recently found that tRNA inhibits the pro-apoptotic activity of cyt c by preventing the interaction of cyt c with the caspase activator Apaf-1. We will investigate the functional interaction between tRNA and cyt c in cancer cell death and to explore the utility of this interaction as a novel therapeutic target. Our central hypothesis is that high levels of tRNA in tumor cells contribute to apoptosis resistance and tumorigenesis, and targeting tRNA is beneficial in tumor therapy. We propose three specific aims: 1) Define the role of tRNA in the intrinsic apoptosis pathway; 2) Investigate the sensitivity of cancer cells to tRNA hydrolysis; and 3) Determine the combined effect of the tRNA-specific RNase Onconase and agents that invoke the intrinsic apoptosis pathway in tumor therapy. The experiments outlined here will improve our understanding of tRNA in the fundamental processes of cell death, and will inform therapies in cancer.